This section provides background information related to the present disclosure which is not necessarily prior art.
Catalytic converters have been useful in motor vehicle exhaust gas systems to convert nitrous oxides, carbon monoxide and/or hydrocarbons to more environmentally friendly compounds. One type of catalytic converter includes one or more ceramic monoliths or substrates mounted inside of a sheet metal housing. The substrates typically contain a multiplicity of longitudinal straight-through-flow exhaust gas passages that are coated with a catalyst.
In many instances, the metal housings used for commercially acceptable converters are formed as “pancake” or “clam shell” designs. These designs include stamped upper and lower shells which are substantially identical to each other. The shells have mating, peripheral side flanges that are welded together along a plane containing the longitudinal axis of the housing. Another commercial form of catalytic housing may be formed from three pieces including a tube with separate end cones welded at each end of the tube.
Other more economically produced catalytic converters may include a singular open-ended metal tube in which the catalyst coated ceramic substrate is inserted. In one method of catalytic converter assembly, the metal tube is radially inwardly compressed around the substrate. In another process, the substrate is pressed into an undersized tube to a fixed position. Regardless of the manufacturing process, care must be taken to avoid damaging the relatively brittle ceramic substrates. Furthermore, substrates that have been cracked or otherwise damaged during assembly are relatively difficult to inspect once the catalytic converter assembly process has been completed and the metal housing substantially precludes access to the substrate. Non-destructive inspection of the completed assembly may not be as reliable as desired. The cost and time associated with post assembly inspection may also be very high. Accordingly, it may be beneficial to provide a non-destructive testing method for detecting substrate fracture during catalytic converter assembly.